As a wiring material applied to an automobile, there has been used an electrical wire in which a conductor made of a twisted wire of soft copper wire is concentrically covered by an insulator. In this field, the amount of the electric wire is increased to satisfy various desired high level functions of the automobile, thus the weight of the electric wire increases. On the other hand, a lighter body of the vehicle is desired, and thinner diameter as well as higher strength of the wire conductor is desired and required.
Precipitation-type alloy wire may be listed as the wire conductor having excellent mechanical and electrical property in order to satisfy the above requirement. When the aging precipitation-type alloy wire is subjected to an aging heat treatment, a certain time period is required to cause the precipitation. Generally, the following furnaces are used:
(1) batch-type annealing furnace (bell type, pot type)
(2) continuous batch-type annealing furnace (bulkhead type, roller hearth type)
Since the wire is wound around the spool and heat-treated in the furnace, or the wire is prepared as stand type or bundle type and heat-treated in the furnace, the productivity of the wire is low in comparison with a continuous annealing apparatus for a single wire.
As a method for annealing wire with high productivity, there are an annealing method in which the wire is continuously passed through a heated annealing furnace, and an annealing method in which current is applied to the wire to generate Joule heat, thereby annealing the wire per se. In both of the above methods, the heat treatment is carried out at a high temperature and for a short time such that the wire may not be subjected to the aging heat treatment.
For example, Japanese Patent Application Publication No. 11-256295 discloses a method for age-treating Cu—Zr alloy while the alloy is passed through a furnace. Japanese Patent Application Publication No. 2000-160311 discloses a method for age-treating Cu—Zr alloy by applying current to the alloy to generate Joule heat.    [Patent document 1] Japanese Patent Application Publication No. 11-256295    [Patent document 2] Japanese Patent Application Publication No. 2000-160311